When designing machine illumination systems, illumination geometry plays a key role in determining the quality of the image and the appearance of the object being observed. It is particularly true of highly specular objects and surfaces which reflect the lighting directly to the observer.
A machine vision engineer must select a lighting geometry which will cause the features of interest to be seen most clearly in the camera's field-of-view. Because specular objects reflect the lighting environment according to their own particular geometry, the selection of the lighting geometry for such applications is especially critical. For example, some applications require lighting from a "high angle", i.e. light supplied at a small angle relative to the optical axis, while other applications require illumination from a "low angle", i.e. light supplied at a much greater angle relative to the optical axis. It is advantageous for the machine vision engineer to have the greatest possible variety of illumination geometries available so as to be able to choose the ideal illumination geometry for any particular illumination application.
Many applications require a radially uniform lighting geometry so that the features of interest will be identically illuminated regardless of their orientation in the field-of-view. Currently, ring lights are available in only a limited variety of angles of incidence. For example, a fiberoptic ring light offers a narrow band of intense illumination with the direction of illumination typically being parallel to or nearly parallel to a central axis of the ring light. An angled reflector ring may be attached to the fiberoptic ring light source in order to redirect the illumination field at a different angle. For example, a ring reflector with a 45.degree. inner reflecting surface immediately under the fiber ring illumination aperture will redirect the light inwardly toward and perpendicular to the central axis of the ring light, creating a "low angle dark field" illumination geometry.
A lighting element ring light consists of a number of light emitting diodes (LEDs) 2 located on a circuit board 4, typically in a circular array around a central aperture 6, as can be seen in FIG. 1. Due to automated manufacturing constraints, the lighting elements 2 must be mounted to a flat circuit board such that the illumination axis, of each mounted lighting element, is perpendicular to the surface of the circuit board 4 and parallel to the central axis A of the manufactured ring light. Alternatively, a long thin circuit board 8 may have a plurality of lighting elements 10 mounted thereon and then the long thin circuit board 8, with a pair of opposed straight lateral edges 12, is bent into a cylindrical shape, as can be seen in FIG. 2, such that the lighting elements are facing inward substantially perpendicular to the central axis A of the ring light.
Automated assembly of lighting elements on circuit boards requires that the lighting elements be placed perpendicular to the circuit board. When the lighting elements are required to project light at any angle other than substantially perpendicular to the circuit board, the lighting elements are individually bent to a desired angle, relative to the circuit board, by laborious hand assembly when the lighting elements are assembled in a fixture and a wiring harness is built up by hand to connect the leads in a desired circuit configuration. Such manual assembly greatly increases the manufacturing costs and reduces the reliability of the finished illumination product. It is desirable for the lighting element illumination circuit to be designed for assembly by a highly reliable automatic positioning and assembly machine in such a manner that the lighting elements can be oriented at any desired angle without intense hand labor.